PostCSS Smart Asset

PostCSS plugin to rebase, inline or copy on url().

Installation

$ npm install postcss postcss-smart-asset

Changes over PostCSS-URL

Changed output of relative URLs so that the harmonize with Webpack. This mainly means that in Webpack world it is pretty common to use relative URLs even inside CSS e.g. use url(./myfile.gif) instead of url(myfile.gif). The last syntax actually lead to some issue during Webpack processing as Webpack would assume that you are referencing an npm package called myfile.gif which is probably not what you thought to do.
Converted whole test suite from Mocha + Chai to Jest. Made whole test suite asynchronous.
Migrated source code to EcmaScript modules (ESM). Refactored internal structure.
Replaced custom eslint definitions with effective linting rules.
Restructured tests to be side-by-side with implementation code.
Use of Preppy instead of custom release logic. Offering a ESM bundle now as well.

Basic example - rebase

// dependencies
const fs = require("fs")
const postcss = require("postcss")
const smartAsset = require("postcss-smart-asset")

// css to be processed
const css = fs.readFileSync("input.css", "utf8")

// process css
const output = postcss()
  .use(
    smartAsset({
      url: "rebase"
    })
  )
  .process(css, {
    from: "src/stylesheet/index.css",
    to: "dist/index.css"
  })

before:

.element {
  background: url("images/sprite.png");
}

after:

.element {
  /* rebasing path by new destination */
  background: url("../src/stylesheet/images/sprite.png");
}

Inline

const options = {
  url: "inline"
}

postcss().use(smartAsset(options)).process(css, {
  from: "src/stylesheet/index.css",
  to: "dist/index.css"
})

before:

.element {
  background: url("/images/sprite.png");
  filter: url("/images/circle.svg");
}

after:

.element {
  /* inlined png as base64 */
  background: url("data:image/png;base64,R0lGODlhAQABAJH/AP///wAAAP///wAAACH/C0FET0JFOklSMS4");
  /* inlined svg as encodeURIComponent */
  filter: url("data:image/svg+xml,%3Csvg xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%2F%3E");
}

Copy

const options = {
  url: "copy",
  // base path to search assets from
  basePath: path.resolve("node_modules/bootstrap"),
  // dir to copy assets
  assetsPath: "img",
  // using hash names for assets (generates from asset content)
  useHash: true
}

postcss().use(smartAsset(options)).process(css, {
  from: "src/stylesheet/index.css",
  to: "dist/index.css"
})

before:

.element {
  background: url("/images/sprite.png");
}

after:

.element {
  /* copy 'sprite.png' from 'node_modules/bootstrap/images/' to 'dist/img/' */
  /* and rename it by hash function */
  background: url("img/a2ds3kfu.png");
}

Muiltiple options

process first matched option by default. multi: true in custom will processing with other options

const options = [
  { filter: "**/assets/copy/*.png", url: "copy", assetsPath: "img", useHash: true },
  { filter: "**/assets/inline/*.svg", url: "inline" },
  { filter: "**/assets/**/*.gif", url: "rebase" },
  // using custom function to build url
  { filter: "cdn/**/*", url: (asset) => `https://cdn.url/${asset.url}` }
]

postcss().use(smartAsset(options))

Checkout tests for examples.

Options combinations

rebase - default
inline
- basePath - path or array of paths to search assets (relative to from, or absolute)
- encodeType - base64, encodeURI, encodeURIComponent
- includeUriFragment - include the fragment identifer at the end of the URI
- maxSize - file size in kbytes
- fallback - copy or custom function for files > maxSize
- ignoreFragmentWarning - do not warn when an SVG URL with a fragment is inlined
- optimizeSvgEncode - reduce size of inlined svg (IE9+, Android 3+)
copy
- basePath - path or array of paths to search assets (relative to from, or absolute)
- assetsPath - directory to copy assets (relative to to or absolute)
- useHash - use content hash of file for naming
- keepName - use filename~hash as filename (assuming useHash is also true)
- hashOptions - options for hash function
custom {Function}
- multi - processing with other options

Options list

`url`

`rebase` - (default)

Allow you to fix url() according to postcss to and/or from options (rebase to to first if available, otherwise from or process.cwd()).

`inline`

Allow you to inline assets using base64 encoding. Can use postcss from option to find ressources.

`copy`

Allow you to copy and rebase assets according to postcss to, assetsPath and from options (assetsPath is relative to the option to).

`url: {Function}`

Custom transform function. Takes following arguments:

asset
- url - original url
- pathname - url pathname (url without search or hash)
- absolutePath - absolute path to asset
- relativePath - current relative path to asset
- search - search from url, ex. ?query=1 from ./image.png?query=1
- hash - hash from url, ex. #spriteLink from ../asset.svg#spriteLink
dir
- from - PostCSS option from
- to - PostCSS option to
- file - decl file path
options - plugin options
decl - related postcss declaration object
warn - wrapped function result.warn for current decl
result – PostCSS result object

And should return the transformed url. You can use this option to adjust urls for CDN.

`maxSize`

(default: 14)

Specify the maximum file size to inline (in kbytes)

`ignoreFragmentWarning`

(default: false)

Do not warn when an SVG URL with a fragment is inlined. PostCSS-URL does not support partial inlining. The entire SVG file will be inlined. By default a warning will be issued when this occurs.

NOTE: Only files less than the maximum size will be inlined.